Traditionally, plasters applied to the body to treat skin lesions or to transdermally deliver drugs to internal lesions or the circulatory system and other organs and other medical adhesives used in medical devices are prepared from polyvinyl alkyl ethers, poly(metha)acrylates, 2-ethylhexyl acrylate-2-ethylhexyl methacrylate copolymers, 2-ethylhexyl acrylate-vinylpyrrolidone copolymers, polyurethane, styrene-isoprene-styrene block copolymers, polyisobutylene rubber, polyisoprene rubber, butyl rubber, natural rubber, silicone resin and other substances. To give a pressure-sensitive adhesion property to these copolymers, known tackifiers, softening agents, fillers, anti-aging agents and other additives are added.
These sticky compositions are required to be safe with little skin irritation and to have well-balanced adhesive properties (tack, adhesion, cohesion). However, none of them meets all these requirements. For example, sticky compositions based on acrylic resin are known to have skin irritancy causing skin sweating, flare or edema. Sticky compositions based on silicone resin are faulty in that the plaster is liable to detaching due to sweating or the plaster becomes more likely to be detached when it is attached to the joint.
In recent years, there have been remarkable progress based on the concept of drug delivery system in the development of transdermal drug delivery preparations aiming at systemic action as well as action on skin lesions. These preparations have been increasingly recognized to be useful as sustained-release preparations. This kind of conventional transdermal drug delivery preparations includes those using a medical adhesive as an adhesive base comprising an adhesive polymer layer as described above which contains a drug and a release aid which promotes the release of the drug on a drug-impermeable backing material. By plastering them on the body, drugs are delivered to diseased parts of the body or to the circulatory system.
The adhesive base for the transdermal drug delivery preparation is required to have high safety and well-balanced adhesive properties and offer good drug release. Particularly in transdermal drug delivery preparations aiming at systemic action, drug release from drug carrier is known to be a key factor. Although the silicone elastomer described above is widely used as a base for implantation preparations and transdermal drug delivery devices and as a drug carrier for various other preparations because it is very safe, it is known to have a problem in drug release in addition to the above-mentioned problems such as the tendency for plaster to be detached due to sweating when it is used as an adhesive base for transdermal drug delivery preparations. In transdermal drug delivery preparations incorporating a silicone elastomer as an adhesive polymer layer, i.e., an adhesive base, the releasing property for the drug retained by the silicone elastomer, i.e., an active ingredient pharmaceutical compound, is very high, provided that the drug has an extremely high vapor pressure like nitroglycerin; and very useful products of devices have been developed. However, the drug releasing property of silicone elastomer is usually very low; therefore, development of devices incorporating the silicone elastomer described above is limited to drugs whose effective dose is low like scopolamine.